1. Technical Field of the Invention
The present invention relates to improving the photostability of at least one dibenzoylmethane sunscreen compound with respect to UV radiation, by intimately admixing therewith an effective photostabilizing amount of a silane or organosiloxane compound bearing a benzylidenecamphor substituent.
2. Description of the Prior Art
It is known to this art that light radiation with wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation with wavelengths more particularly ranging from 280 to 320 nm, i.e., UV-B irradiation, causes erythema and skin burns which can be harmful to the development of a natural tan. For these reasons, as well as for aesthetic reasons, a constant demand exists for controlling this natural tanning and, also, the coloration of the skin; such UV-B radiation should thus be screened from the skin.
It is also known to this art that UV-A irradiation, with wavelengths of from 320 to 400 nm, which tans the skin, is apt to induce an adverse change therein, in particular in the case of sensitive skin or skin which is continually exposed to solar radiation. UV-A radiation in particular causes a loss of elasticity of the skin and the appearance of wrinkles, promoting premature aging. Such irradiation promotes triggering of the erythemal reaction or enhances this reaction in certain individuals and may even be the source of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as conserving the skins"" natural elasticity, for example, an ever-increasing number of subjects wish to control the effect of UV-A rays on their skin. It is thus desirable to also screen UV-A radiation from the skin.
In this regard, one particularly advantageous class of UV-A screening agents currently includes dibenzoylmethane derivatives, and in particular 4-(tert-butyl)-4xe2x80x2-methoxydibenzoylmethane, which have high intrinsic absorption power. These dibenzoylmethane derivatives, which are compounds that are well known per se as screening agents that are active in the UV-A range, are particularly described in FR-A-2,326,405 and FR-A-2,440,933, as well as in EP-A-0,114,607; 4-(tert-butyl)-4xe2x80x2-methoxydibenzoylmethane is moreover commercially available under the trademark xe2x80x9cPARSOL 1789xe2x80x9d from Givaudan.
Unfortunately, it has been determined that dibenzoylmethane derivatives are compounds that are relatively sensitive to ultraviolet radiation (especially UV-A radiation), namely, more specifically, they exhibit an annoying tendency to be degraded more or less rapidly under the influence of such radiation. Thus, this substantial lack of photochemical stability of dibenzoylmethane derivatives in the face of the ultraviolet radiation to which they are by nature intended to be subjected, does not guarantee constant protection during prolonged exposure to the sun, such that, in a restricting manner, repeated applications at regular and close time intervals must be carried out by the user in order to obtain effective protection of the skin against UV radiation.
Thus, EP-A-0,709,080 describes combining dibenzoylmethane derivatives with benzalmalonate derivatives in order to reduce the photoinstability of said dibenzoylmethane derivatives. Nonetheless, the photostabilization of dibenzoylmethane derivatives with respect to UV radiation constitutes, to date, a problem which has not yet been solved completely satisfactorily.
FR-2,607,996 and WO-94/04131 describe combining dibenzoylmethane derivatives with hydrocarbon-based benzylidenecamphor derivatives such as 3-(4-methylbenzylidene)camphor in order to reduce the photoinstability of said dibenzoylmethane derivatives.
Another difficulty, independent of the one indicated above, encountered with dibenzoylmethane derivatives is that these are lipophilic sunscreen agents with the particular feature, and also present the disadvantage of being solid at room temperature. Accordingly, formulating same into antisun cosmetic compositions entails certain constraints as regards their processing, in particular for determining solvents for properly dissolving same, whether alone or in combination with other screening agents. In this regard, oils have been typically employed such as esters, and more particularly C12-C15 alkyl benzoates (xe2x80x9cFinsolv TNxe2x80x9d marketed by Finetex), or triglycerides, and in particular C8-C12 fatty acid triglycerides (xe2x80x9cMiglyol 812xe2x80x9d marketed by Hxc3xcls), but these various products exhibit solubilizing properties with respect to the aforesaid screening agents that remain insufficient.
Sunscreen formulations based on dibenzoylmethane derivatives and on 3-(4-methylbenzylidene)camphor as described in FR-2,607,996 and WO-94/04131 do not obviate this problem of solubility of said dibenzoylmethane derivatives completely satisfactorily.
It has now unexpectedly and surprisingly been found that formulating the dibenzoylmethane derivatives indicated above with an effective amount of a silane or organosiloxane compound containing a benzylidenecamphor substituent, substantially and markedly improves the photochemical stability (or photostability) of these same dibenzoylmethane derivatives.
It has also been determined that the silane or organosiloxane compounds containing a benzylidenecamphor functional group according to the present invention are effective photostabilizing agents, which is also very surprising compared with the known hydrocarbon-based organic screening agents derived from benzylidenecamphor, and constitute a family of solvents which are particularly noteworthy for the screening agents of dibenzoylmethane derivative type such as, for example, 4-(tert-butyl)-4xe2x80x2-methoxydibenzoylmethane; this permits, for an equal amount of solvent, formulating greater amounts of screening agents.
Thus, the present invention features enhancing the stability of at least one dibenzoylmethane compound with respect to UV radiation, by intimately formulating therewith an effective photostabilizing amount of a silane or organosiloxane derivative bearing a benzylidenecamphor substituent.
The cosmetic and/or dermatological compositions according to this invention present the advantage of being particularly photostable, even after prolonged exposure to UV-A and UV-B radiation. Such radiation can be of natural origin (sunlight) or artificial origin (UV lamp).
The present invention, thus, also features formulating a silane or organosiloxane compound containing a benzylidenecamphor functional group into a cosmetic or dermatological composition including at least one dibenzoylmethane sunscreen compound, to enhance the stability of said dibenzoylmethane sunscreen with respect to UV radiation.
More particularly according to the present invention, the subject dibenzoylmethane sunscreens are well known per se and are described, in particular, in FR-A-2,326,405, FR-A-2,440,933 and EP-A-0,114,607.
Consistent herewith, it is intended, of course, to formulate one or more of said dibenzoylmethane compounds into the compositions of the invention.
Among the dibenzoylmethane derivatives suitable for formulation according to the present invention, particularly exemplary are:
2-methyldibenzoylmethane;
4-methyldibenzoylmethane;
4-isopropyldibenzoylmethane;
4-tert-butyldibenzoylmethane;
2,4-dimethyldibenzoylmethane;
2,5-dimethyldibenzoylmethane;
4,4xe2x80x2-diisopropyldibenzoylmethane;
4,4xe2x80x2-dimethoxydibenzoylmethane;
4-tert-butyl-4xe2x80x2-methoxydibenzoylmethane;
2-methyl-5-isopropyl-4xe2x80x2-methoxydibenzoylmethane;
2-methyl-5-tert-butyl-4xe2x80x2-methoxydibenzoylmethane, ;
2,4-dimethyl-4xe2x80x2-methoxydibenzoylmethane;
2,6-dimethyl-4-tert-butyl-4xe2x80x2-methoxydibenzoylmethane; and
4,4xe2x80x2-dimethoxydibenzoylmethane.
Among the dibenzoylmethane derivatives compounds indicated above, most particularly preferred is 4-(tert-butyl)-4xe2x80x2-methoxydibenzoylmethane, in particular that marketed under the trademark xe2x80x9cParsol 1789xe2x80x9d by Givaudan. This sunscreen agent has the following structural formula: 
Another dibenzoylmethane derivative which is preferred according to the present invention is 4-isopropyldibenzoylmethane. This sunscreen agent is marketed under the trademark xe2x80x9cEusolex 8020xe2x80x9d by Merck, and has the following structural formula: 
The subject dibenzoylmethane derivative(s) are advantageously present in the compositions stabilized in accordance with the present invention in contents generally ranging from 0.01% to 10% by weight, and preferably in contents ranging from 0.3% to 5% by weight, relative to the total weight of the composition.
A second compound in the compositions according to the invention comprises a silane or organosiloxane compound substituted by a benzylidenecamphor functional group. These compounds are known to this art and are described, as well as processes for the synthesis thereof, in EP-A-0,325,881, EP-A-0,335,777 and EP-A-0,712,855.
The silane or organosiloxane compound bearing a benzylidenecamphor substituent according to the present invention preferably has the structural formula (I) below: 
in which the radicals R1, which may be identical or different, are each a hydrogen atom, an OH radical, a saturated or unsaturated, linear or branched, C1-C10 alkyl radical, a linear or branched C1-C10 alkoxy radical or an xe2x80x94OSi(CH3)3 radical, with the proviso that two adjacent groups R1 may together form an alkylidenedioxy group in which the alkylidene radical contains 1 or 2 carbon atoms; a is an integer ranging from 1 to 3; A is a hydrogen atom or a radical of formula -L-W such that L is a divalent radical of formula (IIa) or (IIb) below:
xe2x80x94CH2xe2x80x94CHR2xe2x80x94[C(R3)2]mxe2x80x94(CO)nxe2x80x94(O) oxe2x80x94(Z)pxe2x80x94(Y)qxe2x80x94xe2x80x83xe2x80x83(IIa)
xe2x80x94CHxe2x95x90CR2xe2x80x94[C(R3)2]mxe2x80x94(CO)nxe2x80x94(O) oxe2x80x94(Z)pxe2x80x94(Y)qxe2x80x94xe2x80x83xe2x80x83(IIb)
wherein R2 and R3, which may be identical or different, are each a hydrogen atom or a linear or branched C1-C5 alkyl radical, Z is a linear or branched, saturated or unsaturated C1-C6 diyl radical, optionally substituted with a hydroxyl or linear or branched, saturated or unsaturated C2-C8 alkyl radical, Y is xe2x80x94Oxe2x80x94, xe2x80x94NR4xe2x80x94, xe2x80x94SO2NHxe2x80x94, xe2x80x94(CO)Oxe2x80x94, xe2x80x94(CO)NHxe2x80x94 or xe2x80x94O(CO)NHxe2x80x94, wherein R4 is a hydrogen atom or a C1-C5 alkyl radical; m is an integer ranging from 0 to 10; n is 0 or 1; o is 0 or 1; p is 0 or 1; q is 0 or 1; A1 is a hydrogen atom or a radical xe2x80x94L1xe2x80x94W in which the radical L1 has the definition of L, with the proviso that when q=1, then Y represents xe2x80x94SO2NHxe2x80x94, with the further proviso that only one of the two radicals A and A1 is a hydrogen atom; W is a radical of formula (1), (2) or (3) below: 
in which the radicals R6, which may be identical or different, are each a linear or branched C1-C30 alkyl, phenyl, 3,3,3-trifluoropropyl or trimethylsilyloxy radical, at least 80%, by number, of the radicals R6 being methyl radicals; the radicals B, which may be identical or different, are each a radical R6 or a radical X of the formula below: 
in which R1, L, L1 and a are as defined above; r is an integer ranging from 0 to 200, inclusive, and s is an integer ranging from 0 to 50, inclusive, and, if s=0, at least one of the two symbols B is X; u is an integer ranging from 1 to 10, inclusive, and t is an integer ranging from 0 to 10, inclusive, with the proviso that t+u is greater than or equal to 3.
Among the above compounds, particularly preferred is the family of compounds which has at least one, preferably all, of the following characteristics:
R1=H, OCH3, CH3 or two adjacent radicals R1 form a methylenedioxy radical,
R2=H or CH3,
n=0,
q=1.
Among such compounds, preferred are those which have at least one, preferably all, of the following characteristics:
R6 is methyl,
B is methyl,
r ranges from 5 to 20, inclusive,
s ranges from 2 to 15, inclusive,
t+u ranges from 3 to 10, inclusive,
m=1, and
R3 is a hydrogen atom or a methyl radical.
These compounds and the process for preparing same are described, for example, in EP-A-0,335,777.
A second family of preferred compounds comprises the compounds of formula (I) in which s=0.
Exemplary compounds of formula (I) which are particularly preferred are those of the following structural formulae: 
Among the compounds of formula (I), certain of these are novel and constitute another aspect of the present invention.
This is the case for the compounds of formula (I) as defined above in which p is 1 and the radical Z is a linear or branched, saturated or unsaturated C1-C6 diyl radical substituted by a hydroxyl or linear or branched, saturated or unsaturated C2-C8 alkyl radical. Exemplary of these specific compounds is the compound (7) as described above.
Another family of novel compounds of formula (I) includes the silane compounds in which W is a radical of formula (3) and n is equal to 0. Among such compounds, the compounds (10), (11) and (12) as described above are exemplary.
According to the invention, by the expression xe2x80x9ceffective amount of silane or organosiloxane compound bearing a benzylidenecamphor substituentxe2x80x9d is intended an amount which is sufficient to provide an appreciable and significant improvement in the photostability of the dibenzoylmethane derivative(s) contained in the composition. The minimum amount of stabilizer to be formulated, which can vary depending on the nature of the cosmetically acceptable support (vehicle, diluent or carrier) selected for the composition, can be determined without any difficulty via a conventional test for measuring photostability, as described in FR-A-2,607,700.
The silane or organosiloxane compounds bearing a benzylidenecamphor substituent are generally present in the compositions according to the invention at a content at least equal to 0.5% by weight, relative to the total weight of the composition. Even more preferably, this content ranges from 0.5% to 20% by weight relative to the total weight of the composition.
Nonetheless, the cosmetic and/or dermatological compositions of the present invention can contain one or more complementary hydrophilic or lipophilic sunscreens that are active in the UV-A and/or UV-B range (absorbers). These complementary screening agents are advantageously selected from among cinnamic derivatives, salicylic derivatives, benzophenone derivatives, benzotriazole derivatives, benzimidazole derivatives, triazine derivatives, benzalmalonate derivatives, xcex2, xcex2xe2x80x2-diphenylacrylate derivatives, p-aminobenzoic acid derivatives, and the screening polymers and screening silicones described in WO-93/04665. Other examples of organic sunscreens are set forth in EP-A-0,487,404.
The compositions according to the invention can also contain agents for artificially tanning and/or browning the skin (self-tanning agents), such as, for example, dihydroxyacetone (DHA).
The cosmetic and/or dermatological compositions according to the invention can also contain pigments or nanopigments (average size of the primary particles: generally ranging from 5 nm to 100 nm, preferably from 10 to 50 nm) of coated or uncoated metal oxides, such as, for example, nanopigments of titanium dioxide (amorphous or crystallized in rutile and/or anatase form), of iron oxide, of zinc oxide, of zirconium oxide or of cerium oxide, which are all photoprotective agents that are well known per se, which act by physically blocking out (reflecting and/or scattering) the UV radiation. Conventional coating agents are, moreover, alumina and/or aluminum stearate. Such coated or uncoated metal oxide nanopigments are described, in particular, in EP-A-0,518,772 and EP-A-0,518,773.
The compositions of this invention can also comprise conventional cosmetic additives and adjuvants selected, in particular, from among fatty substances, organic solvents, ionic or nonionic thickeners, softeners, antioxidants, anti-free radical agents, opacifiers, stabilizers, emollients, silicones, hydroxy acids, antifoaming agents, moisturizers, vitamins, fragrances, preservatives, surfactants, fillers, sequestering agents, polymers, propellants, basifying or acidifying agents, colorants, dyes or any other ingredient usually used in the cosmetics and/or dermatological field, in particular for the manufacture of antisun compositions in the form of emulsions. Too, any additional ingredient liable to be introduced into the compositions in accordance with the invention must be such that it does not substantially affect or disrupt the photostabilizing effect exerted by the silane or organosiloxane compounds containing a benzylidenecamphor function with respect to the dibenzoylmethane derivatives.
Fatty substances can include an oil or a wax or mixtures thereof. By the term xe2x80x9coilxe2x80x9d is intended a compound which is liquid at room temperature. By the term xe2x80x9cwaxxe2x80x9d is intended a compound which is solid or substantially solid at room temperature and whose melting point is generally greater than 35xc2x0 C.
Exemplary oils include the mineral oils (petroleum jelly); plant oils (sweet almond oil, macadamia oil, blackcurrant pip oil, jojoba oil); and synthetic oils such as perhydrosqualene, fatty alcohols, fatty acids or fatty esters (such as C12-C15 alkyl benzoate marketed under the trademark xe2x80x9cFinsolv TNxe2x80x9d by Finetex, octyl palmitate, isopropyl lanolate, triglycerides, including capric/caprylic acid triglycerides), oxyethylenated or oxypropylenated fatty esters and ethers; silicone oils (cyclomethicone, polydimethylsiloxanes or PDMS) or fluoro oils, and polyalkylenes.
Exemplary waxy compounds include paraffin, carnauba wax, beeswax and hydrogenated castor oil.
And exemplary organic solvents include the lower alcohols and polyols.
The thickeners are advantageously selected, in particular, from among crosslinked polyacrylic acids, and modified or unmodified guar gums and cellulose gums, such as hydroxypropyl guar gum, methylhydroxyethylcellulose and hydroxpropylmethyl cellulose.
The compositions according to the invention are easily formulated according to techniques which are well known to this art, in particular those intended for the preparation of emulsions of oil-in-water or water-in-oil type.
This compositions can be, in particular, in the form of a simple or complex (O/W, W/O, O/W/O or W/O/W) emulsion, such as a cream or a milk, or in the form of a gel or a cream-gel, a powder or a solid tube and can optionally be packaged as an aerosol and can be in the form of a mousse or a spray.
The compositions according to the invention are preferably formulated as oil-in-water emulsions.
When it is an emulsion, the aqueous phase thereof can comprise a nonionic vesicle dispersion prepared according to known techniques (Bangham, Standish and Watkins, J. Mol. Biol., 13,238 (1965), FR-2,315,991 and FR 2,416,008).
The cosmetic and/or dermatological compositions of the invention are useful for protecting the human epidermis or the hair against ultraviolet radiation, as an antisun composition or as a makeup product.
When the cosmetic compositions according to the invention are for protecting the human epidermis against UV rays, or as an antisun (sunscreen) composition, these can be formulated as suspensions or dispersions in solvents or fatty substances, in the form of a nonionic vesicle dispersion or in the form of an emulsion, preferably of oil-in-water type, such as a cream or a milk, in the form of an ointment, a gel, a cream-gel, a solid tube, a stick, a lotion, an aerosol mousse or a spray.
When the cosmetic compositions according to the invention are used for protecting the hair, same can be in the form of a shampoo, a lotion, a gel, an emulsion or a nonionic vesicle dispersion, and can constitute, for example, a rinse-out composition, to be applied before or after shampooing, before or after dyeing or bleaching, before, during or after permanent-waving or straightening the hair, a styling or treating lotion or gel, a blow-drying or hairsetting lotion or gel, or a permanent-waving, straightening, dyeing or bleaching composition for the hair.
When the subject compositions are used as makeup product for the eyelashes, the eyebrows or the skin, such as an epidermal treatment cream, a foundation, a lipstick, an eyeshadow, a face powder, a mascara or an eyeliner, same can be in solid or pasty, anhydrous or aqueous form, such as oil-in-water or water-in-oil emulsions, nonionic vesicle dispersions or alternatively suspensions.
For illustrative purposes, for the antisun formulations in accordance with the invention which contain a support of oil-in-water emulsion type, the aqueous phase (in particular comprising the hydrophilic screening agents) generally constituting from 50% to 95% by weight, preferably from 70% to 90% by weight, relative to the total weight of the overall formulation, the oily phase (in particular comprising the lipophilic screening agents) generally constitutes from 5% to 50% by weight, preferably from 10% to 30% by weight, relative to the entire formulation, and the (co)emulsifier(s) generally represent(s) from 0.5% to 20% by weight, preferably from 2% to 10% by weight, relative to the entire formulation.